Ischemic stroke or acute ischemic stroke (AIS) is typically defined as permanent brain injury secondary to disruption of blood flow. The incidence of AIS is approximately 700,000 per year, with about 61,000 deaths (see Adams et al. Emergency Medicine. Acute Ischemic Stroke: 1072). Although care of the subject with AIS begins with the public recognition and emergency medical system (EMS) instituting an expeditious transport, the formal evaluation and treatment of AIS occurs in the emergency department.
Carotid artery disease occurs when the carotid arteries, located in a person's neck, become narrowed. The carotid arteries are more likely to develop carotid artery disease as a person ages and has risk factors for atherosclerosis, including but not exclusive of hypercholesterolemia, hypertension, diabetes mellitus and tobacco use. Only 1 percent of adults age 50 to 59 have significantly narrowed carotid arteries, but 10 percent of adults age 80 to 89 have this problem.
Arteries are normally smooth and unobstructed on the inside, but as one ages, fat can accumulate in the walls of the artery causing inflammation. This combination leads to the development of a plaque. Plaque is made up of inflammatory and smooth muscle cells as well as cholesterol, calcium, and fibrous tissue. As more plaque builds up, the arteries narrow and stiffen. This process is called atherosclerosis, or hardening of the arteries.
Some plaque deposits are soft and are prone to cracking or forming roughened, irregular areas inside the artery. Cracking, or rupture, of an atherosclerotic plaque exposes material that promotes clot formation to the blood flow. Thus, a large blood clot may then form in the artery, such as in distal common or proximal internal carotid artery or one of its branches. If the clot blocks the artery enough to slow or stop blood and oxygen flow to the brain, it could cause a stroke. More commonly, a piece of the plaque itself, or a clot, breaks off from the plaque deposit and travels through the bloodstream. This particle can then lodge in a smaller artery in the brain and cause a stroke by blocking the artery.
Thus far, the only approved acute pharmacologic intervention for AIS, intravenous alteplase (recombinant tissue plasminogen activator or rtPA). The use of this compound in the emergency department is unique because of its extremely narrow temporal window and strict contraindications, and it has been estimated that just 3%-8% of eligible subjects with AIS receive rtPA.